Lunar sabbatarians like to claim that the ancient Jewish historian Philo kept a lunar sabbath and that it is, in fact, the only kind of weekly sabbath that Philo had ever known.
Here are four quotes from Philo's On the Decalogue that demonstrate he kept the weekly Sabbath on a continuous cycle of seven days, just like we do today. In fact, it appears to me that the lunar sabbath would have been a completely foreign idea to him.
There are in all ten feasts which are recorded in the law. The first, the mention of which may perhaps cause some surprise, is the feast of every day. The second is that held on the seventh day with six days between, called by the Hebrews in their native tongue Sabbath. The third is the new moon which follows the conjunction of the moon with the sun.
The Special Laws, Book II, Chapter XI
Philo wrote that there are six days between each Sabbath. Not sometimes one or two days as required by the lunar sabbath, but six. By listing the new moon after the weekly Sabbath as a separate feast, it also implies that there is no calendrical connection between the new moon and the weekly Sabbath.
After this continuous unbroken feast [of the ordinary day] which has neither beginning nor end, the second to be observed is the sacred seventh day, recurring with six days between.
The Special Laws, Book II, Chapter XV
Philo wrote ordinary days are an unbroken cycle of six days, followed by one day of the Sabbath. Six days and one day. Six days and one day. Six days and one day. Over and over from the beginning of time without break.
For every seventh day is holy, a Sabbath as the Hebrews call it, and it is in the seventh month in every year that the chief of all the feasts falls, and therefore naturally the seventh year also has been marked out for a share in the dignity which belongs to the number.
The Special Laws, Book II, Chapter XIX
The cycle of months must be interrupted from time to time to keep it in sync with the orbit of the earth around the sun and the agricultural cycles caused by that orbit. The weekly Sabbath, however, is never interrupted, so Philo says "every seventh day" and not "the seventh day from the new moon" or anything like that.
For it is from it that the fiftieth day [Shavuot] is reckoned, by counting seven sevens...
The Special Laws, Book II, Chapter XXX
Shavuot, the Feast of Weeks, is seven weeks after the early day of Firstfruits during the week of Unleavened Bread. Starting on the day of Firstfruits, Torah says to count seven weeks and then the next day, the fiftieth day, is Shavuot, the latter day of Firstfruits. Following a lunar sabbath, seven weeks would always amount to greater than fifty days if you count the period between the twenty-eighth day of one month and the seventh day of the next as a single week and less than fifty if you count that period as two weeks.
Addendum: I have also seen lunar sabbatarians appeal to the Jewish Encyclopedia (!?) as evidence that God's weekly Sabbath is based on the phases of the moon. Since the editors and authors of the Jewish Encyclopedia believe that the Bible is a work of fiction and that the Sabbath is a relic of a Mesopotamian moon cult that was only later attributed to YHWH who was a minor Canaanite deity, I wouldn't put much stock in what they have to say on the subject.
